The aims of this study are to evaluate the relationship between air pollution and cardiovascular diseases and specifically to evaluate parameters which may help to elucidate biologic mechanisms by which air pollution may result in cardiovascular disease. Specifically, the study will investigate the relationship between exposure to criteria air pollutants and cardiac autonomic control measured by heart rate variability, cardiovascular reactivity, markers of inflammation and the presence of arrhythmias. The project will also investigate the relationship between ambient air pollution and validated cardiovascular disease including sudden cardiac death, myocardial infarction, CHD and stroke. Air pollution data will be obtained from the US EPA and abstracted into 1, 2, 3 or 6 day mean exposure levels for the dates prior to the individual participant=s clinical exams for baseline and exam 4 of the ARIC study. The ARIC study is a biracial population-based study of cardiovascular disease in 15,792 individuals in four US communities. The baseline examination of the cohort occurred from 1987-1989, with annual recontacts and reexaminations every three years. Numerous biologic measures and health data are obtained at these visits.